Proteinase-activated receptor 2 (PAR2)-activating peptides:: Identification of a receptor distinct from PAR2 that regulates intestinal transport

The effects of PAR(2)-activating PAR(2-)activating peptides, SLIGRL (SL)-NH2, and trans-cinnamoyl-LIGRLO (tc)-NH2 were compared with the action of trypsin, thrombin, and the PAR(1) selective-activating peptide: AlaparafluoroPhe-Arg-cyclohexylAla-Citrulline-Tyr (Cit)-NH2 for stimulating intestinal ion transport. These agonists were added to the serosa of stripped ratjejunum segments mounted in Ussing chambers, and short circuit current (Isc) was used to monitor active ion transport. The relative potencies of these agonists also were evaluated in two bioassays specific for the activation of rat PAR(2): a cloned rat PAR(2) cell calcium-signaling assay (PAR(2)-KNRK cells) and an aorta ring relaxation (AR) assay. In the Isc assay, all agonists, except thrombin, induced an Isc increase, The SL-NH2-induced Isc changes were blocked by indomethacin but not by tetrodotoxin. The relative potencies of the agonists in the Isc assay (trypsin >> SL-NH2 > tc-NH2 > Cit-NH2) were strikingly different from their relative potencies in the cloned PAR(2)-KNRK cell calcium assay (trypsin >>>tc-NH2 congruent to SL-NH2 >>>Cit-NH2) and in the AR assay (trypsin >>>tc-NH2 congruent to SL-NH2). Furthermore, all agonists were maximally active in the PAR(2)-KNRK( cell and AR assays at concentrations that were one (PAR(2) -activating peptides) or two (trypsin) orders of magnitude lower than those required to activate intestinal transport. Based on the distinct potency profile for these agonists and the considerable differences in the concentration ranges required to induce an Isc effect in the intestinal assay compared with the PAR(2)-KNRK and AR assays, we conclude that a proteinase-activated receptor, pharmacologically distinct from PAR(2) and PAR(1) is present in rat jejunum and regulates intestinal transport via a prostanoid-mediated mechanism.